Imaging in Acute Facial Nerve ParalysisM Castillo, MD, FACR

Department of RadiologyUniversity of North Carolina, Chapel Hill

Overview of PresentationIntroductionReview of facial nerve anatomyClinical and Imaging features of Bells palsyTypical AtypicalOther causes of acute facial paralysis

IntroductionBells palsy accounts for 75% of cases of acute facial nerve (7th cranial nerve) paralysisImaging is not needed in majority of patients unless they have atypical features W/atypical features, MR & CT may demonstrate potentially treatable lesions affecting facial nervesFacial nerves can be affected anywhere along their course

Anatomy ReviewFacial nerve nuclei lie in reticular formation of brainstem, ventral to floor (tegmentum) of 4th ventricle(4)Motor Nuclei:Efferent fibers surround nuclei of CN VI & form small mounds on floor of 4th ventricle (facial colliculi)Non-Motor Nuclei:SalivatorySolitary

Facial colliculus

Efferent fibers surround 6th CN nucleus & exit at cerebellopontine angle (CPA)7th nerve courses into internal auditory canal (IAC) Within superior anterior quadrant(6)

AntPost

Exits IAC via Fallopian canalNarrowest point throughout entire course Felt to be culprit in facial nerve compression in Bells palsy & other causes of nerve swelling

Fallopian Canal

Progress to geniculate ganglionGives rise to greater superficial petrosal nerveContains taste axons from tongue & somatic fibers

Geniculate ganglion

Fibers then course posteriorly under lateral semicircular canal in middle ear (tympanic portion)Fibers angle back & inferiorly at second genu diving the descending canalHere last somatic & parasympathetic fibers separate from facial nerve via the chorda tympani nerveTympanic PortionMastoid segment

Facial nerve exits skull base at stylomastoid foramenFacial nerve angles superiorly & anteriorly behind posterior margin of vertical mandibular ramusJust before entering parotid gland, inferior branches originatePosterior auricular, digastric & stylohyoidWithin substance of parotid gland, superior branches ariseTemporal, zygomatic, buccal, orbicularis oris, mandibular & cervical

Clinical Signs Suggesting Site of Facial Nerve Lesion

Upper facial territory is supplied by bilateral motor corticesLower facial territory is supplied only by contralateral motor cortexTherefore, unilateral central lesions spare upper faceLesions distal to geniculate ganglionMostly motor abnormalitiesLesions proximal to geniculate ganglion Motor, gustatory & autonomic abnormalities

Typical Bells PalsyIncidence 1530 per 100,000Usually during winterEtiology not entirely understoodPossibly viral (Herpes Simplex Virus) or idiopathicViral infection of facial nerve results in demyelination, inflammation & swellingTraps nerve in narrow confines of fallopian canalDiagnosis of exclusionMade only when clinical & imaging (if necessary) findings are supportive

Typical Bells PalsyUsually a clinical diagnosisAcute onset unilateral (lower or upper) facial paralysis, posterior auricular pain, decreased tearing, hyperacusis (30%) & disturbances of tasteBy physical examination, Bells palsy divided according to classification by House and BrackmanGrades 1 & 2 have better outcomes with worse outcome as grade increases.80-90% recover completelyOver age 60, only 40% recover completely

Imaging in Typical Bells PalsyImaging in typical Bells palsy is not usually necessaryWhen necessary, MRI is bestNormal facial nerve distal to geniculate ganglion may enhanceFacial nerve proximal to geniculate ganglion does not normally enhanceIn patients with Bells palsy, enhancement of facial nerve in fallopian & ICA is typical

C/o Dr. M. Michel, Wisconsin

Atypical Bells PalsyClinical featuresSlower onset of symptomsBilateralRecurrenceNumbness is not unusualProgression beyond seven days suggests another cause

Imaging in Atypical Bells PalsyC/o Dr. M. Michel, Wisconsin

Alternative Causes of Acute Facial Nerve ParalysisAtypical signs & symptoms which suggest etiology other than Bells palsy require imagingClinical history is crucial in distinguishing etiologiesChoice of imaging technique depends on clinical suspicion

Lyme DiseaseLyme disease (borreliosis)Endemic areas (Northeast USA, central Europe, Scandinavia, Canada)Consider in children w/atypical facial palsyImaging: small white matter lesions similar to multiple sclerosis, enhancement of facial & other cranial nervesBilateral facial paralysis: 25%Important to make diagnosis early because it is curable early w/antibiotics

Ramsay Hunt SyndromeCaused by reactivation varicella zoster virus (herpes virus type 3)Facial paralysis + hearing loss +/- vertigoHerpes zoster oticusTwo-thirds of patients have rash around earOther cranial nerves, particularly trigeminal nerves (5th CN) often involvedWorse prognosis than Bells (complete recovery: 50%)Important cause of facial paralysis in children 6-15 years old

C/o Dr. M. Michel, Wisconsin

Infectious causesAcute facial paralysis may result from bacterial or tuberculous infection of middle ear, mastoid & necrotizing otitis externaIncidence of facial paralysis with otitis media: 0.16%Infection extends via bone dehiscences to nerve in fallopian canal leading to swelling, compression & eventually vascular compromise & ischemiaImmune compromised patients are at risk for pseudomona infectionPoor prognosis (complete recovery is < 50%)

Tuberculosis

Parotid & peri-parotid disease

HIV Infection

Bezolds abscess & coalescent mastoiditis

TraumaMost acute post traumatic facial palsies are due to t-bone fracturesHistorically fractures classified as longitudinal or transverse with transverse carrying risk of permanent paralysisLongitudinal fracture usually leads to temporary paralysis from concussion & swelling of nerveTransverse fracture can lead to transection of nerveIn all types of paralysis due to fracture, usually the region of geniculate ganglion is involved

Neoplasms27% of patients with tumors involving the facial nerve develop acute facial paralysisMost common causes: schwannomas, hemangiomas (usually near geniculate ganglion) & perineural spread such as with head and neck carcinoma, lymphoma & leukemiaOther neoplasms can also involve the facial nerveAdults: metatstatic disease, glomus tumors, vestibular schwannomas & meningiomasChildren: eosinophilic granuloma & sarcomas

Hemangioma

Hemangioma

Facial Nerve Schwannoma

Perineural Tumor Spread

Glomus TumorGlomus tumors arising from jugular bulb (jugulare) and/or middle ear (tympanicum) may involve the facial nerve

Other tumorsRhabdomyosarcoma & squamous cell carcinoma of the EAC

Vestibular Schwannoma

Common tumor

However, facial nerve is resistant to compressionTherefore, tends to produce facial paralysis mostly when they attain a large size

Vestibular Schwannoma-Common tumor-However, facial nerve is resistant to compression, thus, tends to produce facial paralysis mostly when they attain a large size

MeningiomaSecond most common primary tumor of cerebellopontine angleRarely results in facial paralysis

Rhabdomyosarcoma

Miscellaneous Causes

Hypertrophic PolyneuropathyHypertrophic polyneuropathies occasionally lead to facial paralysis

Wegeners Granulomatosis

Other CausesGuillain-Barre SyndromeAscending paralysisIatrogenicTemporal bone surgeryExcision of vestibular schwannoma has 90% recovery

Melkersson-Rosenthal Syndrome Acute episodes of facial paralysisFacial swellingFissured tongueScrotal tongueVery rareFamilial but sporadicUsually begins in adolescenceLeads to facial disfigurementNo definite therapy

ConclusionWhile Bells palsy does not typically require imaging for diagnosis, imaging evaluation is important in the work-up of patients with atypical or unusual presentations of acute facial nerve paralysis, identification of discreet lesions may lead to a change in management of these patients.